Process for recovering polyhydroxyalkanoates using centrifugal fractionation

ABSTRACT

The present invention relates to a process for recovering polyhydroxyalkanoate from a biological source material containing the polyhydroxyalkanoate, the process comprising: a) comminuting the biological source material; b) suspending the comminuted biological source material in a fluid; c) partitioning the polyhydroxyalkanoate from the other components of the biological source material by centrifugal fractionation to form a solid-solid separation; and d) recovering the polyhdroxyalkanoate.

This is a continuation of application Ser. No. 08/251,828, filed on Jun.1, 1994 now abandoned.

TECHNICAL FIELD

The present invention relates to processes for isolating specific resincomponents from other biomass components. More specifically, the presentinvention relates to a process for the recovery of apolyhydroxyalkanoate from a biological system, such as a plant orbacteria, by using centrifugal fractionation.

BACKGROUND

Commodity polymers are typically produced from petrochemical sources bywell-known synthetic means. However, recent advances in technology haveresulted in the promise of new sources of commodity polymers.Particularly promising is the production of plastic resins using livingorganisms ("bioplastic"), including genetically manipulated bacteria andcrop plants, which are designed to produce polymers such aspolyhydroxyalkanoate (PHA); a number of bacteria which naturally producePHA are also promising sources of PHA. (see for example, NOVELBIODEGRADABLE MICROBIAL POLYMERS, E. A. Dawes, ed., NATO ASI Series,Series E: Applied Sciences--Vol. 186, Kluwer Academic Publishers (1990);Poirier, Y., D. E. Dennis, K. Klomparens and C. Somerville,"Polyhydroxybutyrate, a biodegradable thermoplastic, produced intransgenic plants", SCIENCE, Vol. 256, pp. 520-523 (1992)). In a largescale production, for example agricultural production, the harvestingand purifying of such bioplastic from the biomass debris is a criticalstep for determining the practical feasibility of such technology.

The separation of polymeric lipids such as PHA from a large-scalebiological source, such as an agricultural crop, is not a trivial task.The conventional separation methods used extensively in the extractionof low molecular weight lipids are not practical to employ in a resinisolation process. For example, a simple mechanical press is impracticalbecause, unlike separating vegetable oils from oil-seeds, solid plasticscannot be squeezed out of crops by mechanical pressing.

Solvent extraction is also impractical for a number of reasons. Asolution of polymer develops an extremely high viscosity, even atrelatively low concentration, thereby making the solution extremelydifficult to work with. Furthermore, the stripping of solvent frompolymer is a slow and difficult process. A commonly used solvent for theextraction of PHA from bacteria is chloroform. However, the use of alarge amount of such a solvent, potentially harmful to health andenvironment if accidentally released, near the harvesting site would beundesirable.

Separation of PHA by sedimentational methods should be, in principle,possible. However, simple gravitational (1-G force) settling in a liquidsuspending medium is, in fact, quite impractical. The rate of settlingis extremely slow. In addition, such slow settling is easily disruptedby the Brownian motion of the fine PHA particles induced by the thermalfluctuation of the suspending fluid molecules surrounding the particles.Furthermore, the extended period of time required to settle very finePHA particles introduces the problem of bacterial contamination andsubsequent biodegradation of the particle suspension.

Based on the foregoing, there is a need for a simple and economicalprocess for recovering bioplastics from a large-scale biological source.Such a process would preferably be easily adaptable as an integral partof the agricultural production of bioplastics.

It is therefore an object of the present invention to provide a processfor recovering bioplastics from a biological source material.

SUMMARY

The present invention relates to a process for recoveringpolyhydroxyalkanoate from a biological source material containing thepolyhydroxyalkanoate, the process comprising: a) comminuting thebiological source material; b) suspending the comminuted biologicalsource material in a fluid; c) partitioning the polyhydroxyalkanoatefrom the other components of the biological source material bycentrifugal fractionation to form a solid-solid separation; and d)recovering the polyhdroxyalkanoate.

DETAILED DESCRIPTION

The present invention answers the need for a process for recoveringbioplastics from a biological source material.

The following is a list of definitions for terms used herein.

"g/sec" means grams per second.

"g/min" means grams per minute.

"μ" means micron(s).

"psi" means pounds per square inch.

"MPa" means mega pascal, which is equivalent to about 145 psi.

"Fractionation" means the separation and/or isolation of components of amixture. The invention described herein preferably achieves suchfractionation due to differences in the density and/or particle size ofthe various components.

"Solid-solid separation" and "solid-solid fractionation" mean theseparation or partitioning of components in a sample wherein eachfraction comprises a component in a solid state. For example, aseparation resulting in a fraction comprising PHA granules suspended ina fluid medium and a fraction comprising other insoluble biomass isconsidered a solid-solid separation.

"Liquid-solid separation" and "liquid-solid fractionation" mean theseparation or partitioning of components in a sample wherein at leastone fraction contains an otherwise solid component in liquid state, andat least one fraction comprises a component in a solid state. Forexample, a separation resulting in a fraction comprising PHA dissolvedin a solvent and a fraction comprising other insoluble biomass isconsidered a liquid-solid separation.

"Polyhydroxyalkanoate" and "PHA" mean a polymer having the followinggeneral structure: ##STR1## wherein R is preferably an alkyl or alkenyl,m is 1 or 2, and n is an integer. The structure enclosed in brackets iscommonly referred to as a repeating unit. The terms polyhydroxyalkanoateand PHA include polymers containing one or more different repeatingunits. Examples of preferred PHAs recoverable by the present processincluded those disclosed in U.S. Pat. No. 5,489,470, Noda, issued Feb.6, 1996; World Patent Application 95/20621, Noda, published Aug. 3,1995; World Patent Application 95/20615, Noda, published Aug. 3, 1995;and U.S. Pat. No. 5,292,860, Shiotani and Kobayashi, issued Mar. 8,1994.

"Recovering polyhydroxyalkanoate from a biological source material", inaddition to referring to the recovery of the particular PHA produced bya biological source material which produces a single PHA, also refers tothe recovery of one or more types of PHA when the biological sourcematerial produces more than one type of PHA.

"Alkyl" means a carbon-containing chain which may be straight, branchedor cyclic, preferably straight; substituted (mono- or poly-) orunsubstituted; and saturated.

"Alkenyl" means a carbon-containing chain which may be straight,branched or cyclic, preferably straight; substituted (mono- or poly-) orunsubstituted; and monounsaturated (i.e., one double or triple bond inthe chain), or polyunsaturated (i.e., two or more double bonds in thechain, two or more triple bonds in the chain, or one or more double andone or more triple bonds in the chain).

"Comprising" means that other steps and other ingredients which do notaffect the end result can be added. This term encompasses the terms"consisting of" and "consisting essentially of".

All percentages are by weight of total composition unless specificallystated otherwise.

The present invention relates to a process for recovering (i.e.,isolating) polyhydroxyalkanoate from a biological source materialcontaining the polyhydroxyalkanoate, the process comprising centrifugalfractionation of the biological source material such that thepolyhydroxyalkanoate is partitioned from the other components of thebiological source material by solid-solid separation.

PHA components found in biological systems (e.g., conventional, orgenetically engineered bacteria or genetically engineered plants) tendto settle at rates different from other cellular components such asproteins and carbohydrates when they are suspended in a common fluidmedium. The difference in the sedimentation rate results in the spatialsegregation of mixed particulates into multiple layers (fractionation)each containing predominantly a single component.

According to the Stokes'law of sedimentation, there are two majorfactors affecting the sedimentation rates of particles: differences inthe density and size of suspended particles. These factors independentlycontrol the separation efficiency of the fractionation process.

Density is an intrinsic property of the material to be separated.Generally, there is no easy way of manipulating the density of anindividual component to be fractionated. The density difference betweenparticles in a composition is not always large enough to achievesubstantial fractionation of one component from the rest. When thedensities of the components are sufficiently different, a high degree ofseparation can be achieved, particularly when a suspending medium havingan intermediate density is used. The density of PHA is sufficientlydifferent from other biomass components, such as proteins andcarbohydrates, to achieve some degree of fractionation.

Differences in particle size also contribute greatly to theeffectiveness of the fractionation process. PHA is generally stored inbiological systems in the form of very fine granules having a diameterof about or below 1μ. The particle size of PHA granules are thereforemuch smaller as compared to other cellular components from the disruptedcell. In addition, particle size can be further manipulated by apost-harvest processing which includes grinding or colloid-milling.Specific types of biological source material and the process arediscussed in more detail below.

Biological Source Material

Sources from which PHA is recovered via the process of the presentinvention include single-cell organisms such as bacteria or fungi andhigher organisms such as plants (herein collectively referred to as"biological source material" or "BSM"). While such BSM could bewild-type organisms, they are preferably genetically manipulated speciesspecifically designed for the production of a specific PHA of interestto the grower. Such genetically manipulated organisms are produced byincorporating the genetic information necessary to produce PHA.Typically, such genetic information is derived from bacteria whichnaturally produce PHA.

Plants useful in the present invention include any geneticallyengineered plant designed to produce PHA. Preferred plants includeagricultural crops such cereal grains, oil seeds and tuber plants; morepreferably, avocado, barley, beets, broad bean, buckwheat, carrot,coconut, copra, corn (maize), cottonseed, gourd, lentils, lima bean,millet, mung bean, oat, oilpalm, peas, peanut, potato, pumpkin, rapeseed(e.g., canola), rice, sorghum, soybean, sugarbeet, sugar cane,sunflower, sweetpotato, tobacco, wheat, and yam. Such geneticallyaltered fruit-bearing plants useful in the process of the presentinvention include, but are not limited to apple, apricot, banana,cantaloupe, cherries, grapes, kumquat, lemon, lime, orange, papaya,peaches, pear, pineapple, tangerines, tomato, and watermelon. Preferablythe plants are genetically engineered to produced PHA pursuant to themethods disclosed in Poirier, Y., D. E. Dennis, K. Klomparens and C.Somerville, "Polyhydroxybutyrate, a biodegradable thermoplastic,produced in transgenic plants", SCIENCE, Vol. 256, pp. 520-523 (1992),World Pat. Application 95/05472, Somerville, Nawrath and Poirier,published Feb. 23, 1995; and World Pat. Application 93/02187,Somerville, Poirier and Dennis, published Feb. 4,1993. U.S. Pat. No.5,650,555, Dennis et al., issued Jul. 22, 1997, and U.S. Pat. No.5,610,041, Nawrath et al., issued Mar. 11, 1997. Particularly preferredplants are soybean, potato, corn and coconut plants geneticallyengineered to produce PHA.

Bacteria useful in the present invention include any geneticallyengineered bacteria designed to produce PHA, as well as bacteria whichnaturally produce PHA. Examples of such bacteria include those disclosedin NOVEL BIODEGRADABLE MICROBIAL POLYMERS, E. A. Dawes, ed., NATO ASISeries, Series E: Applied Sciences--Vol. 186, Kluwer Academic Publishers(1990); U.S. Pat. No. 5,250,430, Peoples and Sinskey, issued Oct. 5,1993; U.S. Pat. No. 5,245,023, Peoples and Sinskey, issued Sep. 14,1993; U.S. Pat. No. 5,229,279, Peoples and Sinskey, issued Jul. 20,1993; and U.S. Pat. No. 5,149,644, Lubitz, issued Sep. 22, 1992.

It is preferable that the BSM contain a sufficient quantity of PHA tomake the process economically desirable. Preferably, the initial contentof PHA in the source material should be at least about 5% of the totaldry weight; more preferably at least about 25%; more preferably at leastabout 50%; more preferably still, at least about 75%.

Isolation Process

The process of the present invention preferably involves the followingunit-operation steps: pretreatment, size reduction, suspension, andcentrifugal separation. The optimal range of unit operation conditionsor individual devices will vary considerably according to the type ofraw BSMs used.

The pretreatment of source materials comprising PHA is preferred inorder to remove low molecular weight contaminants readily soluble inappropriate solvents, such as sugars, oils and sometimes moisture. Avariety of standard pretreatment methods used for the processing of foodcrops are known to those skilled in the art and may be readily employedfor the pretreatment step of the present invention. Examples of suchpretreatment steps include oil extraction (for example, see BAILEY'SINDUSTRIAL OIL AND FAT PRODUCTS, THIRD ED., Johne Wiley and Sons: NewYork (1964), pp. 663-713), water washing (for example, see U.S. Pat. No.2,881,076, Sair, issued Apr. 7, 1959), and alcohol washing (for example,see Eldridge, A. C., W. J. Wolf, A. M. Nash and A. K. Smith, "AlcoholWashing of Soybean Protein", AGRICULTURAL AND FOOD CHEMISTRY,July-August, 1963, pp. 323-328).

The pretreated material comprising PHA granules is then pulverized(e.g., dry milling) to small fragments, by first using, for example acommon vibratory or hammer mill. The pulverization of source material bydry milling, particularly for agricultural crop plants comprising PHAgranules, preferably produces grain flour of a particle size finer thanabout 500μ in diameter, more preferably finer than about 300μ, morepreferably still, finer than about 100μ.

The comminuted material is then dispersed in a suspending fluid such aswater, chlorinated carbon solvents (e.g., chloroform, carbontetrachloride, or dichlorethane), various organic solvents (e.g.,ethanol, methanol, acetone, methyl ethyl ketone, ethyl acetate, hexane,heptane, pentane, or mixtures thereof), or supercritical fluids (e.g.,carbon dioxide or nitrous oxide); preferably water. If the suspendingfluid is water, the water is preferably heated to promote hydration ofcertain non-PHA components prior to the wet milling to a temperaturepreferably not exceeding 90° C. If a suspending medium having anintermediate density between the PHA and other biomass is desired, thenthe suspending medium is preferably an aqueous solution of an organic orinorganic salt, or an aqueous solution of a water-soluble sugar. Usefulorganic salts include, but are not limited to, potassium glycolate,potassium citrate, potassium lactate, potassium malate, and dipotassiumtartrate. Useful inorganic salts include, but are not limited to, sodiumchloride, potassium chloride, calcium chloride, magnesium chloride, andcalcium sulfate. Useful water-soluble sugars include, but are notlimited to, sucrose, glucose, and raffinose.

The material is further treated by wet milling using a device such as acolloid mill, sonicator, or homoginizer, to obtain the desired particlesize distribution for the dispersed solids. For wet milling, thecomminuted material is suspended in a fluid. Preferred fluids include,but are not limited to water; ethanol; and aqueous solutions of organicsalts, inorganic salts or sugars. The wet milling should preferablyproduce suspensions having an average particle size of smaller thanabout 50μ.

The suspension mixture of PHA and other biomass components is thenprocessed with a centrifugal device to fractionate PHA-rich particlesfrom the other biomass. Preferred centrifugal devices include, but arenot limited to, centrifuge, ultracentrifuge, or hydrocyclone separator.An industrial scale centrifugal separation device may be used in theprocess of the present invention for fractionation of the PHA, so longas the device provides sufficient "G" force (i.e., sedimentational forcefield created, for example, by centrifugal effect expressed in terms ofthe equivalent to gravitational force) to achieve the sedimentation ofsolid particles above the rate necessary to overcome the Brownian motionof particles to be settled. The centrifugal force field employed in theprocess of the present invention is preferably at least about 10 G(i.e., ten times faster than simple gravimetric settling) to achieverapid and efficient fractionation of PHA from other biomass components.More preferably, the centrifugal force field is at least about 100 G,more preferably at least about 1,000 G. more preferably at least about10,000 G, more preferably still at least about 100,000 G.

In one embodiment of the present invention, a hydrocyclone is employedas the centrifugal device. A hydrocyclone consists of a conical cavitywith an eccentric inlet port and two exit ports above and below theconical cavity. The vortex flow created by the off-centered high-speedinjection of fluid creates a centrifugal force resulting in thesedimentation of heavy particles toward the inner wall of the conicalcavity. The heavier portion will exit predominantly from the smaller tipof the cone, while the lighter portion will exit from the wider part ofthe cone. The centrifugal force field increases in a hydrocyclone withthe inlet feed rate and decreases with the diameter of the conicalcavity. For example, in a typical 1 cm diameter hydrocyclone, it ispossible to achieve well above 100 G of centrifugal force by maintainingthe feed rate of suspension above several tens of gallons per minute.(See, for example, Day, R. W., "Hydrocyclones in Process and PollutionControl", CHEMICAL ENGINEERING PROGRESS, Vol. 69, pp. 67-72 (1973); andU.S. Pat. No. 2,754,968, Vegter and Hage, issued Jul. 17, 1956; andKIRK-OTHMER ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, THIRD ED., Vol. 12, pp.1-29, John Wiley and Sons, (1990)). Hydrocyclones useful in the presentinvention are available from a variety of manufactureres includingDorr-Oliver, Inc. (Milford, Conn.), Yardney Water Management Systems,Inc. (Riverside, Calif.), and Quality Solids Separation Co. (Houston,Tex.).

In another embodiment of the present invention, a continuous centrifugemay be employed as the centrifugal device. A continuous centrifugecomprises a rapidly rotating cylinder having a feed suspension flowinginside the cylinder. As a result of the rotation, centrifugal force iscreated thereby promoting sedimentation of heavier components toward theinner wall of the rotating cylinder. The sedimentate is continuouslycollected by a scraping mechanism while the supernatant is removed aseffluent. A typical industrial scale centrifuge operating at severalthousand rpm can easily produce a centrifugal force well above 100 G.(See, for example, Ambler, C. M., "The Evaluation of CentrifugePerformance", CHEMICAL ENGINEERING PROGRESS, Vol. 48, pp. 150-158,(1952); and KIRK-OTHMER ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, THIRD ED.,Vol. 12, pp. 1-29 John Wiley and Sons, (1990)). Centrifuges useful inthe present invention are available from a variety of manufacturers,including Humboldt Decanter, Inc. (Atlanta, Ga.), Western States MachineCo. (Hamilton, Ohio), and Bird Machine Co. (South Walpole, Mass.).

Preferably, the process of the present invention yields at least about70% of the PHA in the source material, more preferably at least about80%, more preferably still at least about 90%.

Preferably, at least about 85% of the dry mass of the PHA-rich fractionisolated by the process of the present invention is PHA, more preferablyat least about 95%, more preferably still at least about 99%.

The PHAs recovered by the process of this invention are useful forforming a variety of plastic articles, including those disclosed in U.S.patent application Ser. No. 08/187,969, Noda, filed Jan. 28, 1994; U.S.Pat. No. 5,489,470, Noda, issued Feb. 6, 1996; World Patent Application95/20621, Noda, published Aug. 3, 1995; World Patent Application95/20615, Noda, published Aug. 3, 1995. Such plastic articles include,but are not limited to, films, sheets, foams, fibers, nonwovens,elastomers, adhesive and molded articles. Such plastic articles can befurther incorporated into a variey of useful products including, but notlimited to, personal cleansing wipes; disposable health care productssuch as bandages, wound dressings, wound cleansing pads, surgical gowns,surgical covers, surgical pads; other institutional and health caredisposables such as gowns, wipes, pads, bedding items such as sheets andpillowcases, foam mattress pads.

The following non-limiting examples illustrate the methods of thepresent invention.

EXAMPLE 1 Isolation of Poly(3-hydroxybutyrate-co-3-hydroxyoctanoate)from Soybeans

Soybeans, from a genetically altered soybean plant, comprisingpoly(3-hydroxybutyrate-co-hydroxyoctanoate) are roll milled to form thinflakes. The low molecular weight lipids and oils contained in the flakesare initially removed by pressing the flakes. The remaining lowmolecular lipids and oils are subsequently extracted from the flakes byusing hexane as a solvent. The resulting defatted soybean flakes aredried and pulverized using a vibratory energy mill (Sweco, Florence,Ky.) to produce a flour having an average particle size of less than80μ. The flour is then hydrated in water at 65° C. for 30 minutes toproduce a suspension containing 7% solids by weight. The suspension isthen passed through a colloid mill (Littleford Day, Florence, Ky.) onceto assure complete mixing. The suspension is then passed through ahomogenizer (Model 3M, APV Gaulin, Willimington, Mass.) operated at8,000 psi, two times, to produce a suspension mixture consisting of finegranules of polymer having an average particle size of less than 1μ andother soybean biomass debris comprising proteins and carbohydrates. Thehomogenized suspension of soybeans is fed to a hydrocyclone (DOXIETYPE-A, Dorr-Oliver, Milford, Conn.) with a heavy duty pump (Model4678-10S, Northern Pump, Minneapolis, Minn.) at a feed rate of 150 g/secunder a nominal pressure of 3 MPa. The effluent stream coming out thetop section of the hydrocyclone contains most of the polymer granules.This portion of the suspension is spray dried and washed with 40%water/60% ethanol mixture to remove soluble residual components such assugars, to produce a cake of poly(3-hydroxybutyrate-co-hydroxyoctanoate)granules with a purity of greater than 95%, and a yield of about 85%with respect to the starting material.

EXAMPLE 2 Isolation of Poly(3-hydroxybutyrate-co-hydroxyhexanoate) fromMaize

Grains of maize (corn), from a genetically altered maize plant,comprising poly(3-hydroxybutyrate-co-3-hydroxyhexanoate are hammermilled to form meals. The low molecular weight lipids and oils containedin the meals are removed first by pressing the flakes and are thenfurther extracted by using hexane as the solvent and washed with 40%water/60% ethanol mixture to remove other soluble components such assugars. The resulting defatted and desugared maize meals are dried andcomminuted using a vibratory energy mill (Sweco, Florence, Ky.) toproduce a flour having an average particle size of less than 80μ. Theflour is then hydrated in water at 65° C. for 30 min to produce asuspension containing 7% solids by weight. The suspension is then passedthrough a colloid mill (Littleford Day, Florence, Ky.) once to assurecomplete mixing. The suspension is then passed twice through ahomogenizer (Model 3M, Gaulin, Willmington, Mass.) operated at 8,000 psito produce a suspension mixture consisting of fine granules ofpoly(3-hydroxybutyrate-co-3-hydroxyhexanoate having an average particlesize of less than 1μ and other maize biomass debris comprising proteinsand carbohydrates. The homogenized suspension of soybeans is fed to acontinuous centrifuge (6" Solid Bowl Centrifuge, Bird Machine Co., SouthWalpole, Mass.) at a feed rate of 1,500 g/min. The supernatant effluentstream coming out the continuous centrifuge is spray dried to produce acake of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate granules with apurity higher than 98%, and a yield of about 85% with respect to thestarting material.

EXAMPLE 3 Isolation of Poly(3-hydroxybutyrate-3-hydroxyvalerate) fromTobacco

Tobacco leaves, from a genetically altered tobacco plant, comprisingpoly(3-hydroxybutyrate-co-3-hydroxyvalerate) are hammer milled to form aflour. The low molecular weight soluble components contained in theflakes are removed by washing first with hexane and then with a 40%water/60% ethanol mixture to produce a dry flour having an averageparticle size of less than 80μ. The flour is then hydrated in water at65° C. for 30 min to produce a suspension containing 7% solids byweight. The suspension is then passed through a colloid mill (LittlefordDay, Florence, Ky.) once to assure complete mixing. The suspension isthen passed twice through a homogenizer (Model 3M, Gaulin, Wilmington,Mass.) operated at 8,000 psi to produce a suspension mixture consistingof fine granules of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) havingan average particle size of less than 1μ and other tobacco biomassdebris. The homogenized suspension of tobacco is fed to a continuouscentrifuge (6" Solid Bowl Centrifuge, Bird Machine Co., South Walpole,Mass.) at a feed rate of 1,500 g/min. The supernatant effluent streamcoming out the continuous centrifuge is spray dried to produce a cake ofpoly(3-hydroxybutyrate-co-3-hydroxyvalerate) granules with a purityhigher than 95%, and a yield of about 85% with respect to the startingmaterial.

EXAMPLE 4 Isolation of Poly(3-hydroxybutyrate-co-3-hydroxydecanoate)from Coconuts

Coconuts, from a genetically altered coconut tree, comprisingpoly(3-hydroxybutyrate-co-3-hydroxydecanoate) are shredded to form thinflakes. The low molecular weight lipids and oils contained in the flakesare extracted by using hexane as a solvent. Soluble sugars are alsoremoved by using a 40% water/60% ethanol mixture. The resulting defattedand desugared coconut flakes are dried and pulverized using a vibratoryenergy mill (Sweco, Florence, Ky.) to produce a flour having an averageparticle size of less than 80μ. The flour is then hydrated in water at65° C. for 30 min to produce a suspension containing 7% solids byweight. The suspension is then passed through a colloid mill (LittlefordDay, Florence, Ky.) once to assure complete mixing. The suspension isthen passed twice through a homogenizer (Model 3M, Gaulin, Wilmington,Mass.) operated at 8,000 psi to produce a suspension mixture consistingof fine granules of poly(3-hydroxybutyrate-co-3-hydroxydecanoate) havingan average particle size of less than 1μ and other coconut biomassdebris. The homogenized suspension of coconuts is fed to a hydrocyclone(Doxie Type-A, Dorr-Oliver, Milford, Conn.) with a heavy duty pump(Model 4678-10S, Northern Pump, Minneapolis, Minn.) at a feed rate of200 g/sec under a nominal pressure of 4 MPa. The effluent stream comingout the top section of the hydrocyclone will contain most of thepoly(3-hydroxybutyrate-co-3-hydroxydecanoate) granules. This portion ofthe suspension is spray dried to produce a cake ofpoly(3-hydroxybutyrate-co-3-hydroxydecanoate) granules with a purityhigher than 95%, and a yield of about 85% with respect to the startingmaterial.

EXAMPLE 5 Isolation of Poly(3-hydroxybutyrate-co-3-hydroxyheptanoate)from Potatoes

Potato flakes, from potatoes obtained from a genetically altered potatoplant, comprising poly(3-hydroxybutyrate-co-3-hydroxyheptanoate) arewashed with water and then hydrated at 65° C. for 30 min to produce asuspension containing 7% solids by weight. The suspension is then passedthrough a colloid mill (Littleford, Day, Florence, Ky.!) once to assurecomplete mixing. The suspension is then passed twice through ahomogenizer (Model 3M, Gaulin, Wilmington, Mass.) operated at 8,000 psito produce a suspension mixture consisting of fine granules ofpoly(3-hydroxybutyrate-co-3-hydroxyheptanoate) having an averageparticle size of less than 1μ and other potato biomass debris. Thehomogenized suspension of potato is fed to a continuous centrifuge (6"Solid Bowl Centrifuge, Bird Machine Co., South Walpole, Mass.) at a feedrate of 1,500 g/min. The supernatant effluent stream coming out of thecontinuous centrifuge is spray dried to produce a cake ofpoly(3-hydroxybutyrate-co-3-hydroxyheptanoate) granules with a purityhigher than 95%, and a yield of about 85% with respect to the startingmaterial.

EXAMPLE 6 Isolation of Poly(3-hydroxybutyrate) from A. eutrophus

A culture of A. eutrophus which naturally producespoly(3-hydroxybutyrate) is treated with an ultrasonic sonicator (BransonUltrasonics Corp., Danbury, Conn.) to produce a suspension mixtureconsisting of fine granules of poly(3-hydroxybutyrate) having an averageparticle size of less than 1μ and other bacterial biomass debriscontaining about 20% solids by weight. The homogenized suspension ofbacterial components is fed to a hydrocyclone (Doxie type-A,Dorr-Oliver, Milford, Conn.) with a heavy duty pump pressure of 4 MPa.The effluent stream coming out the top section of the hydrocyclonecontains most of the poly(3-hydroxybutyrate) granules. This portion ofthe suspension is spray dried to produce a cake ofpoly(3-hydroxybutyrate) granules with a purity higher than 95%, and ayield of about 90% with respect to the starting material.

EXAMPLE 7 Isolation of Poly(3-hydroxybutyrate) from E. Coli

A culture of E. coli which has been genetically manipulated to producepoly(3-hydroxybutyrate) is treated with an ultrasonic sonicator (BransonUltrasonics Corp., Danbury, Conn.) to produce a suspension mixtureconsisting of fine granules of poly(3-hydroxybutyrate) having an averageparticle size of less than 1μ an other bacterial biomass debriscontaining about 5% solids by weight. The homogenized suspension ofbacterial components is fed to a hydrocyclone (Doxie type-A,Dorr-Oliver, Milford, Conn.) with a heavy duty pump pressure of 4 MPa.The effluent stream coming out the top section of the hydrocyclonecontains most of the poly(3-hydroxybutyrate) granules. This portion ofthe suspension is spray dried to produce a cake ofpoly(3-hydroxybutyrate) granules with a purity higher than 95%, and ayield of about 90% with respect to the starting material.

All publications and patent applications mentioned hereinabove arehereby incorporated in their entirety by reference.

It is understood that the examples and embodiments described herein arefor illustrative purposes only and that various modifications or changesin light thereof will be suggested to one skilled in the art and are tobe included in the spirit and purview of this application and scope ofthe appended claims.

What is claimed is:
 1. A process for recovering polyhydroxyalkanoatefrom a biological source material containing the polyhydroxyalkanoate,the process comprising:(a) comminuting the biological source material;(b) suspending the comminuted biological source material in a suspendingfluid having a substantially uniform density wherein the density of saidsuspending fluid is not intermediate between the polyhydroxyalkanoateand the other components of the biological source material; (c)partitioning the polyhydroxyalkanoate from the other components of thebiological source material by centrifugal fractionation to form asolid-solid separation, said solid-solid separation being rate driven byboth particle size and density; and (d) recovering thepolyhydroxyalkanoate.
 2. The process of claim 1, wherein the biologicalsource material is plant material.
 3. The process of claim 2, whereinthe centrifugal fractionation is carried out by a hydrocyclone.
 4. Theprocess of claim 2, wherein the centrifugal fractionation is carried outby centrifugation.
 5. The process of claim 2, wherein the biologicalsource material is avocado, barley, beets, broad bean, buckwheat,carrot, coconut, copra, corn, cottonseed, gourd, lentils, lima bean,millet, mung bean, oat, oilpalm, peas, peanut, potato, pumpkin,rapeseed, rice, sorghum, soybean, sugarbeet, sugar cane, sunflower,sweetpotato, tobacco, wheat, yam, apple, apricot, banana, cantaloupe,cherries, grapes, kumquat, lemon, lime, orange, papaya, peaches, pear,pineapple, tangerines, tomato, or watermelon.
 6. The process of claim 5,wherein the biological source material is soybean.
 7. The process ofclaim 5, wherein the biological source material is corn.
 8. The processof claim 5, wherein the biological source material is potato.
 9. Theprocess of claim 1, wherein the biological source material is bacteria.10. The process of claim 9, wherein the centrifugal fractionation iscarried out by a hydrocyclone.
 11. The process of claim 9, wherein thecentrifugal fractionation is carried out by centrifugation.